Myotonic dystrophy (DM1) is the most common adult onset muscular dystrophy in humans. Currently, there is no cure or an FDA approved drug for DM1 and related diseases. DM1 is an autosomal dominant disorder resulting from the expansion of a CTG-repeat sequence in the 3' untranslated region of the DMPK gene. This defect results in the expression of mutant DMPK RNAs encoding expanded CUG repeats (CUGexp) that form large intra nuclear RNA-protein complexes or foci. Expression of CUGexp RNAs leads to abnormal RNA splicing, which in turn has been linked to the development of key features of DM1 pathology. We hypothesize that small molecules that degrade or disperse CUGexp RNAs in DM1 cells can re-establish normal splice patterns and reverse DM1 pathology. To test this hypothesis, we have developed a primary HTS and a secondary hit validation assay to identify small-molecules that selectively alter the biology of DMPK CUGexp RNAs without affecting the normal DMPK transcripts. Our in house library was developed using a robust machine learning chemoinformatics platform and consists of 40,000 highly diverse small-molecules representing a library of several million compounds. Preliminary results obtained from a screen of 2,500 compounds demonstrate that our strategy allows the rapid identification of potent molecules that successfully reverse DM1 pathology in both patient cells and DM1 mouse models. In a concerted effort to identify a set of potent lead compounds that can be developed as a therapeutic cocktail for DM1 we propose the following Aims: Aim 1. Implement primary HTS and the secondary hit validation assay to screen 20,000 molecules from our in-house library. Aim 2. Test hits in tertiary DM1 patient cell-based assays to identify highly potent leads that reverse five key cellular DM1 phenotypes. Selectivity, toxicity and synergy of leads will be measured in parallel. Aim 3. The chemical structure of lead compounds will be reiteratively refined to optimize pharmacological properties and establish structure-activity relationships.